It doesn't necessarily matter. It all depends on how the rasterizer resolves the non integer pixels in that particular position. I've had results where visuals on the left side of the screen look fine, but an integer translation to the right side of the screen show a missing pixel.
Unless the text is moving, it's generally a good idea to resolve the position to integers just prior to rendering. If nothing else it's quick test. Do this...
mySpriteBatch.DrawString(myFont, "blahblah", myPosition.ToPoint().ToVector2());
See if that makes the problem go away. If it doesn't, you've got other issues